The present invention refers to an electronic switching power supply system for air-conditioning devices to be installed inside motor vehicles.
The air-cooling of the vehicle passenger compartment, when the vehicle is parked, is greatly limited by the lack of an autonomous source that supplies electric energy when the engine is switched off.
In fact, the amount of electric energy supplied by the storage battery already present in the vehicle is insufficient to guarantee such air-cooling for a prolonged period of time.
On the other hand, it would be extremely useful to implement such a system in the motorcars, in order to obtain undoubted advantages in terms of comfort for the user of the vehicle; furthermore, the existing air-conditioning system in the vehicle could be made even more efficient, with respect to the known art, by minimizing the amount of heat to dispose of at the ignition of the engine.
The installation of a photovoltaic cell on the roof of the vehicle, in the form of a solar panel, partially enables the difficulties mentioned above to be overcome, since the fan of the air-conditioning device is powered by the energy supplied by the solar panels.
However, since, for economic reasons, the same electric motor of the fan is used, and said fan is also powered by the storage battery of the vehicle, it is necessary to interpose at least one energy device adapter between the motor and the solar panel, in such a way as to use the available electric energy efficiently, allowing for the fact that oscillations of available power are produced, caused by the variations of the sun radiation and of the temperature of the panel.
FIG. 1 shows a Cartesian drawing of the V-I characteristics of a solar panel for traditional motorcar use, wherein, on the axis of abscissas, the voltage values (V) are indicated in Volt and, on the axis of ordinates, the current intensity values (I) are indicated in Ampere.
It is evident that such a solar panel is similar to a current generator substantially up to the axis indicated by A, i.e. just next to the knee-point of the curves, which are shown in the Cartesian diagram of FIG. 1.
In said FIG. 1, there is a point in the characteristic curve, indicated by the letter G, equal to a radiation flow of 700 W/m2 and to a temperature of about 25 degrees centigrade, wherein the panel has its maximum energy efficiency.
The locus of the points of maximum energy efficiency, that is given by the product of the output voltage with the output current, when the radiant incident power changes, is, by good approximation, a vertical straight line (isovoltage, indicated by the letter X in FIG. 1), while, by changing the temperature, the locus of the points of maximum energy efficiency is a horizontal straight line (isocurrent).
Further, in the Cartesian diagram of FIG. 1, a point of maximum efficiency at the temperature of 65xc2x0 C. is indicated with the letter H.
It can be demonstrated that the efficiency decreases by about 0.5% per each Kelvin grade.
Allowing that the direct current electric machines with a commutator are optimised to function to a given supply voltage, when the power supply is an element with an elevated dynamic impedance, such as a current generator, as in the case of a solar panel, the panel-motor system functions in low efficiency conditions, which are worsened in conditions of low sun irradiation.
To overcome this inconvenience, a direct current converter is interposed between the solar panel and the motor, as shown in FIG. 2, wherein a block corresponding to the solar panel is indicated by number 13, a block corresponding to the motor by number 4, and a block corresponding to the direct current converter by number 2.
A power output control device , indicated by the number 3 in FIG. 2, can be interfaced with the wiring of the vehicle, which is indicated generally by 6.
Such embodiments were necessary, to improve the energy match, however, this type of solution is expensive in economic terms and in terms of overall size and weight.
Furthermore, it is necessary to consider, in the global energy balance, the conversion losses inevitably introduced by the direct current converter 2.
Finally, to work the system at the maximum efficiency point, it is necessary to provide a temperature sensor on panel 13, which inevitably, increases the production costs.
In conclusion, if the converter 2 is fitted in the proximity of the solar panel 13, as is usually done in motorcars, an elevated value of current intensity passes through the wiring resistance 5, thereby lowering the system efficiency.
A purpose of the present invention is to overcome the above mentioned inconveniences, and to provide a power supply system of an electronic switching electric motor for air-conditioning devices to be installed inside the vehicles. In order to have the maximum use of the available energy at the output terminals of the solar panel to power the motor, the system may be configured without interposing any electronic conversion or electronic control device between the two objects.
Another purpose of this invention is to realise a power supply system of an electronic switching electric motor, without using expensive components or complex technologies.
Such objectives are achieved by a power supply system of an electronic switching electric motor for air-conditioning devices to be installed inside the motor vehicles made in accordance with the present invention as disclosed herein.
Using the operating characteristics of an electronic switching motor with a double machine, that uses, in its electronic control unit, a microprocessor and a very low friction method of rotor suspension, it is possible to obtain the power supply system as claimed in claim 1, using the aforesaid electronic switching motor in two different operating modes, one relative to the system powered by the storage battery and by the traditional electric system found in motor vehicles, the other relative to a power generated by a solar panel.
The switching between the two operating modes is automatic and it does not require any additional components nor signals from an external source, as it uses an electromagnetic relay that is already present in the traditional type of an electronic switching motor.